Manufacture of petroleum coke

ABSTRACT

Clusters of petroleum coke pellets are made by the steps of dispersing particulate carbon seed particles in a high boiling petroleum oil, heating the seeded oil in a coking heater under conditions of controlled cracking, and introducing the effluent from the heater into a coke drum where the seed particles serve as nucleating agents in the formation of clusters of petroleum coke pellets.

United States Patent Schlinger et al.

[ June 27, 1972 MANUFACTURE OF PETROLEUM COKE Inventors: Warren G.Schlinger, Pasadena, Calif.;

Harold C. Kaufman, Houston, Tex.

Assignee: Texaco Inc., New York, NY.

Filed: June 9, 1969 Appl. No.: 831,548

US. Cl ..208/l31, 44/10, 44/20,

23/2092 Int. Cl ..C10g 9/14 Field of Search ..208/46, 50, 106, 131;

References Cited UNITED STATES PATENTS 9/1944 Hemminger Bogart et al..::.20s/s0 2,717,865 Kimberlin et al. ..208/1 31 2,775,549 12/1956 Shea..208/l31 X 3,022,246 2/1962 Moser.. ..208/127 3,116,231 12/1963 Adee....208/46 3,338,817 8/1967 Zrinscak et al. ....208/46 3,460,907 8/1969Winsett.... ....23/209.1 3,524,806 8/1970 Case ..208/46 PrimaryExaminer-Edward J. Meros Attorney-K. E. Kavanagh, Thomas H. \Vhaley andCarl G. Ries [5 7] ABSTRACT 3 Claims, 1 Drawing Figure MANUFACTURE OFPETROLEUM COKE BACKGROUND OF THE INVENTION 1 Field of the Invention Thisinvention relates to an improvement in the manufacture of petroleumcoke. More specifically it relates to producing clusters of petroleumcoke pellets by an improved delayed coking process.

2. Description of the Prior Art Regular petroleum coke as made by thewell known delayed coking process consists of dehydrogenated andcondensed hydrocarbons of high molecular weight in the form of a uniformunsubdivided matrix of considerable physical extent containing dispersedthroughout petroleum based aliphaticlike compounds.

In the regular delayed coking process, oil is charged into afractionating tower. The bottoms from the fractionating tower are heatedand introduced into a coke drum where coke is formed. Coke made by theregular delayed coking process is amorphous and generally soft. Further,the density of such material is low, its porosity is high, and it isweak in compression. Accordingly, such coke may be unsatisfactory foruse in metallurgical processes, such as for example in a blast furnacewhere coke beds must support without crushing the weight of upper bedscontaining iron ore and limestone.

SUMMARY This invention pertains to a process for manufacturing clustersof petroleum coke pellets which are characterized by unusually highcompressive strength, high density, and low porosity. More particularly,the invention relates to the discovery that fused clusters of petroleumcoke pellets from about one thirty-second to one-fourth diameter may beformed by heating in a coking heater under controlled thermal crackingconditions a high boiling liquid petroleum feedstock containingdispersed throughout minute seed particles such as particulate carbonsoot or a combination of particulate carbon soot and catalyst fines. Thepartically cracked effluent from said coking heater is introduced into acoke drum where petroleum coke pellets are produced and areconsolidated, forming clusters of coke pellets and balls ranging indiameter from about 1 to 6 inches.

The principal object of this invention is to produce clusters ofspheroidal shaped solid petroleum coke pellets of improved compressivestrength by cracking and polymerizing a high boiling liquid petroleumfeedstock containing seed particles, e.g., carbon soot or particulatecarbon plus catalyst fines.

This and other objects will be obvious to those skilled in the art fromthe following disclosure.

DESCRIPTION OF THE INVENTION Feedstream According to the process of thepresent invention a conventional coking heater may be charged with afeedstream of high boiling liquid petroleum feed taken from the bottomsof a vacuum tower or a fractionator; for example, the bottoms from adistillation column fed with petroleum liquids such as virgin crude,reduced crude, heavy slops and naphthas, residual fuel oil, decanted oilfrom a catalytic cracker, heavy fuel oil slurry, heavy gas oils, andmixtures thereof. Included in said feedstream to the coking heater isabout 0.01 to about 0.5 weight percent or higher particulate carbon.Amounts above 0.5 weight percent do not materially enhance the process.The particulate carbon may be added to the high boiling liquidfeedstream as dry particulate carbon soot; or it may be part of aresidue slurry of particulate carbon in fuel oil which is supplied tosaid fractionator as part of the feed.

Such a fuel oil-particulate carbon slurry may be prepared by the carbonrecovery process described in US. Pat. No. 2,992,906 issued to Frank E.Guptill, Jr. In said process, very fine carbon particles entrained inthe gaseous products of reaction of fossil fuels and oxygen areseparated from the product gas by scrubbing the gaseous products withwater,

forming a particulate carbon-water slurry. This particulate carbon-waterslurry is contacted with alight liquid hydrocarbon, forming a slurry ofparticulate carbon in light liquid hydrocarbon. A heavy liquidhydrocarbon e.g., fuel oil, is then mixed with said light liquidhydrocarbon carbon slurry and then the light liquid hydrocarbon isdistilled off leaving said slurry residue of particulate carbon soot inheavy fuel oil. Altemately, the particulate carbon-light liquidhydrocarbon slurry may be fed to the fractionator.

Electron micrographs of the carbon soot particles show that theyresemble small spheres of sponge like" texture that may range in sizefrom about 0.01 to 0.5 microns but which are usually about 70millirnicrons in'diameter. Because of this structure the carbon has atremendously high surface area, for example from about 300 to 1,000square meters per gram. Particulate carbon soot is both oleophilic andhydrophilic. 1 gram of soot will absorb about 2 to 3 cc. of oil. Atypical analysis of the particulate carbon soot comprises in weightpercent: carbon 92 to 94, hydrogen 0.4 to 1.1, sulfur 0.3 to 0.6, andash 3.4 to 4.7.

In another embodiment of this invention the feedstream to the cokingheater may contain about 0.003 weight percent or more of catalyst finesin addition to the aforesaid particulate carbon. The catalyst fines maybe added to and mixed with the high boiling liquid feedstream to thecoking heater; or the catalyst fines may be part of the decanted oilwhich is supplied to said fractionator as part of the fresh feed. Forexample, fresh feed to the fractionator may contain up to about 30weight percent of fluid cracked heavy cycle gas oil from a catalyticcracker regenerator, also known as FCHCGO (Decanted Oil). About 0.04 to0.40 pounds or more of catalyst fines may be present in each gallon ofFCHCGO oil charged. The bulk of the fines have a particulate size rangeof about 1 to microns. Composition of the catalyst may be approximately50 percent aluminum oxide (Al- O )-with the bulk of the remainder beingsilicon dioxide.

The effluent from off the top of the coke drum comprising essentiallyhydrocarbon vapors and optionally a comparatively small amount of watervapor is also charged into the fractionator.

Fractionator The fractionator for producing the high boiling liquidpetroleum feed is operated at a pressure in the range of 7 to 12 psigand a temperature in the range of 275 to 750 F. Pressure gas oil yieldsfrom the fractionator amount to about 60 to 65 weight percent, basisfresh feed to fractionator, and include light, intermediate, and heavygas oils varying individually with end point specifications. Otherproducts from the fractionator include: propylene and butylenefeedstocks (about 1 to 3.5-weight percent), light and heavy naphthas(about 10 to 18 weight percent), and fuel gas (about 1 to 5 weightpercent).

Feedstreams to the fractionator which have a high salt content may bedesalted by conventional desalting techniques in order to prevent thefouling of heat exchange surfaces and the plugging of heater tubes. Forexample, the crude feedstock may be intimately mixed with water,caustic, and a demulsifying agent to dissolve salt and bottoms sediment.Water is then electrostatically separated from the oil, carrying alongthe inorganic impurities. The caustic and demulsifant aid in theseparation.

Vacuum Tower The bottoms from the fractionator containing essentiallyall of the aforesaid carbon soot and catalyst fines may be introduceddirectly into a coking heater or preferably into a conventional vacuumdistillation tower where under a vacuum of about 19 to 30 mm of mercuryfurther separation of the lighter components from the charge stock iseffected. With the vacuum tower on-stream, the total gas oil yield(pressure gas oil vacuum gas oil) will be greater than the gas-oil yieldwithout a vacuum tower in the line.

Besides maximizing the gas-oil yield, the vacuum tower alters thecomposition of the feed to the coking heater in the next step, e.g.,increases specific gravity, viscosity, ash content and concentration ofseed particles. The effect of operating with the vacuum tower in theline as compared to operating without the vacuum tower and dischargingthe bottoms from thedistillation tower directly into the coking heateris shown in Table 1. Most of the properties of the charge stock to thecoking heater increase when the vacuum tower is in the line. Further,the effect on the product is beneficial as the coke pellets appear finerand unite better in a cluster.

TABLE I [Effect of vacuum tower operation on charge stock to cokingheater] High boiling High boiling petroleum petroleum oil made oil madewithout vacwith vacuum uum tower tower operin line (fracating(vactionator uum tower Property bottoms) bottoms) Gravity, API 8. -12. 03. 0-7.0 Sp. gr. at 60 F 0. 086-1. 014 1. 022-1. 052 Sulfur, wt.percent 1. 2-1. 1. 5-2. 0 Basic N p.p.m 3, GOO-4,000 5, 000-6, 000Viscosity, SFS at 210 F 200-600 500-1, 000 Salt content, grams/bbl. -20-40 Ash, wt. percent 0. 03-0. 07 0. 05-0. 10 Conradson carbon, wt.percent 11. 0-14. 0 17. 0-22. 0 Metals, p.p.m.:

Ni 45-65 60-80 V 60-75 75-100 F 70-85 90-120 Free carbon soot content,wt. percent..- 0 04-0. 10 0. 12-0. 28 Catalyst content, ll)./gal 0003-0. 04 0. 006-0. 06 Watson characterization factor, K,. 10. 0-10. 810. 4-10. 7 Hydrogen to carbon weight ratio, min- 0 11-0. 110 0. 10-0.108 Boiling point at 10 mm., 10% overhead,

Optionally present (equal parts by weight of A110; and SiOr).

Coking Heater The coking heater serves as a thermal cracking reactor.The charge to the coking heater may be the seeded hot heavy residuumfrom the bottom of the vacuum tower or from the, bottom of thefractionator. The coking heater charge in weight percent (basis freshfeed charged to the fractionator) is in the range of about 53 to 66 withthe vacuum tower on and about 74 to 94 with the vacuum tower down. Highboiling residuums having the desired composition may be also introducedinto the process at this point.

The coking heater may comprise an externally fired heating coil of suchdesign as to effect a rapid heating of the oil to a predeterminedtemperature and a minimum soaking time, thereby controlling the crackingof the oil while it is in the coil. In the cracking reaction, largemolecules are split into two or more smaller molecules. Thermal crackingstarts at a temperature of about 750 F. and the rate of reaction doublesfor every F. increase in reaction temperature. Polymerization andcondensation reaction wherein two molecules combine to form a largermolecule are prevented from proceeding in the coil to the point wherecoke is formed. Rather, such solid forming reactions are delayed untilthe effluent from the coking heater is charged into the coke drum.

The coking heater may be one of conventional design wherein the feed isheated from an inlet temperature in the range of about 650 to 720 F. toa sufficiently high temperature so that thermal cracking occurs at arapid rate. However, residence time is controlled and kept to a minimumso that only about percent of the thermal cracking is completed in thecoil.

The coking heater outlet temperature is controlled at a temperature inthe range of 900 to 930 F. Higher temperatures may cause rapid coking inthe coking heater and shorten on stream time. Lower temperatures producesoft coke with a high VCM (volatile combustible matter) content.

The residence time in the tubular heater must be long enough to bringthe oil up to the desired temperature. However, excess time in thetubular heater may cause coking and result in clogging the heater coil.Thus, the residence time in the tubular coil is maintained at about 1 to3 minutes (preferably less than 2 minutes) while at the previously.mentioned conditions of temperature and pressure.

One method for controlling the velocity, and residence time in theheating coil is by injecting a relatively small amount of liquid waterinto the high boiling petroleum oil feed entering the heating coil.Water injection is controlled at a rate sufficient to maintain the oilvelocity in the heating coil high enough to prevent coke from formingand depositing in the heater coil. For example, the amount of liquidwater injected into the high boiling liquid petroleum feed may vary fromabout 0.3 to 4.0 weight percent (basis oil charged to the cokingheater).

Coke Drums The hot efiluent from the coking heater may comprise highboiling liquid petroleum and cracked compounds of said high boilingliquid petroleum, hydrocarbon vapors, and a comparatively small amountof water vapor. The effluent is introduced into a coke drum at atemperature in the range of 880 to 895 F. and a pressure in the range ofabout 40 to 60 psig. The coke drum is stationary and consists of avertical elongated cylinder having a truncated cone-shaped section atthe lower end. The charge is fed to the coke drum axially at the bottomand passes through a deflector assembly mounted on the bottom headinside the coke drum. The deflector assembly consists of a shortcylinder with a closed top and with eight elongated vertical slotsequally spaced around the walls. These slots divide the charge intoeight separate streams. Each stream emerges radially from a slot andthen swirls upwardly as directed by the conical shaped sides which formthe end section of the vessel.

As the charge fills the coke drum, petroleum coke pellets form andcombine in clusters, in a manner to be further described. Hydrocarbonvapors at a temperature in the range of 810 to 820 F. and a pressure inthe range of about 20 to 45 psig leave from the top of the coke drum andflow into the fractionator, along with a comparatively small amount ofwater vapor, if any.

While the exact mechanism by which the petroleum coke pellets are formedand clustered is unknown, it may be postulated that in the coke drum theparticulate carbon soot dispersed in the substantially liquid charge mayserve as seeds or nucleating agents on which the hydrocarbons condense,polymerize, and crosslink. Under time-temperature conditions in thecoking zone the resulting deposit on the surface of a seed particle oron a growing coke particle undergoes dehydrogenation and the formationof a layer of coke. Repetition of this coking cycle causes successivelayers of coke to build-up on the growing particle.

Initially, the particulate carbon soot seed and the growing particleswill be in suspension in the upwardly swirling feedstream within thecoke drum. However, at some point, pellet sized particles will settleout by gravity and deposit on and fuse with other coke pellets at thebottom of the coke drum, forming a cluster of petroleum coke pellets.The pellets harden and the level of the coke bed raised until a batch ofclustered petroleum coke pellets fills the coke drum.

In appearance, the petroleum coke pellet clusters may take on severalforms. For example, in a preferred embodiment of the invention with thevacuum tower in the line, the subdivided spheroidal shaped petroleumcoke pellets about onethirty-second to one-fourth inches in diameter arefused to contiguous pellets to form a cluster. In another form, thepetroleum coke pellets are partially fused to contiguous pellets andpartially bonded to each other by means of from about 2 to 30 weightpercent of a solid asphaltic-like material as produced along with thepellets during the coking of said high boiling petroleum oil. Avariation of this last form consists of spheroidal shaped clusters ofsaid fused and bonded petroleum coke pellets wherein the diameter of thespheroid is about 1 to 6 inches and the outer surface is smooth.

When a coke drum has been filled with a batch of hardened coke clustersto a desired level, it is taken out of service and decoked. First,superheated steam is put into the coke drum at the bottom, to displacehydrocarbon vapors and to remove high boiling point hydrocarbonsremaining on the coke. Then, after the coke drum has been steamed for asufficient length of time, e.g., about 1 to 3 hours to producespecification VCM coke, the coke drum is filled with water and cooled.The water is then drained from the cooled coke drum, and the top andbottom heads are removed. An axially aligned hole is cut verticallythrough the coke bed to permit the introduction of high pressure jetstreams of water. By this means, the batch of petroleum coke is brokenup into lumps and removed from the bottom of the drum.

The coke yield, basis weight percent of coking heater charge is in therange of 20 to 26 with the vacuum tower on and from about 17 to 21 withthe vacuum tower down.

The petroleum coke produced by the process of our discovery ischaracterized by the properties shown in Table 11. When tested by meansof a Chatillion light spring tester, a oneeighth inch diameter pelletwill withstand a compressive load of 17 pounds average and about 14pounds minimum. In comparison, a comparable sized piece of regularpetroleum coke will fail at a compressive load of 8 pounds average andabout 6 pounds minimum. Further, the petroleum coke does not degradeduring handling; that is, there is no increase in fines nor other sizingchanges during movement and stockpiling.

Undersirable adulterating products may be removed from the petroleumcoke by calcining the coke in a rotary kiln at a temperature in therange of about l,000 to l,500 C.

TABLE ll Properties of Spheroidal Petroleum Coke Clusters DESCRIPTION OFTHE DRAWING A more complete understanding of the invention may be had byreference to the accompanying schematic drawing which shows thepreviously described process in detail. Although the drawing illustratesa preferred embodiment of the process of this invention, it is notintended to limit the invention to the particular apparatus or materialsdescribed.

With reference to the drawing, fresh feed consisting of heavy slops andnaphtha in line 1, a mixture of crude oils, fuel oil, and if presentdecanter oil from a catalytic cracker containing catalyst fines in line2, and slurry oil containing particulate carbon from a synthesis gascarbon recovery system in line 3 are introduced into fractionator 4.Coke drum vapor and optionally a comparatively small amount of steamfrom coke drums 5 and 6 are also introduced into fractionator 4 by wayof line 7.

Over a temperature range of about 275 to 750 F. and a pressure range ofabout to 25 psig the aforesaid feed is separated into various productstreams. For example, the following streams are taken from thefractionating tower: light, intermediate and heavy gas oils throughlines 8, 9 and 10 respectively. Overhead products such as the followingare removed through overhead line 11: propylene and butylene feedstock,light and heavy naphtha, water, and fuel gas.

In a'preferred embodiment, with valve 12 closed and valve 13 opens thebottoms from fractionator 4 at a temperature in the range of about 710to 725 F. and a pressure of about 12 psig are passed through line 14, 15and 16 into vacuum tower l7. Vacuum gas oil is removed from the vacuumtower through lines 18 to 21. Vacuum residuum, at a pressure of about 30mm of mercury and a temperature in the range of about 600 to 690 F. isremoved from the bottom of vacuum tower 17 through lines 22 to 24 andvalve 25.

By means of pump 26, line pressure is increased to about 300 to 600 psigand the vacuum residuum is passed through lines 27 and 28 and intocoking heater 29. Liquid water maybe injected into the high boilingpetroleum oil in line 27 by way of lines 30 and 31. Metering valve 32controls the rate of water injection.

From line 33 at the exit of coking heater 29, the hot effluent at anexit temperature in the range of about 900 to 930 F.

and a pressure in the range of about 40 to 60 psig is passed into cokedrum 5 by way of lines 34 to 36, and control valve 37. While coke drum 5is being filled, valve 38 is closed and coke drum 6 is being decoked.After coke drum 5 has been filled, valve 37 is closed, valve 38 isopened, and coke drum 6 is filled by way of lines 33, 39, 40 and 41while drum 5 is being decoked.

The efiluent from coking heater 29 enters at the bottom of coke drum 5,emerging through eight vertical slots, for exampic 42 and 43, in theside wall of deflector assembly 44. Similarly, during the filling ofcoke drum 6, the effluent from coking heater 29 emerges through eightvertical slots, for example, 45 and 46, in the side walls of deflectorassembly 47.

During the filling of coke drum 5, overhead valves 48 and 49 are closedand valve 50 is opened. Hydrocarbon effluent vapors and perhaps acomparatively minor quantity of steam are removed from the top of cokedrum 5 and are introduced into fractionator 4 as previously described,by way of lines 51 to 53 and line 7. Similarly, while coke drum 6 isbeing filled valves 50 and 54 are closed, valve 49 is opened, andoverhead effluent vapors from coke drum 6 are sent to the fractionatorby way of lines 55 to 57, and line 7.

Steaming of the coke to control its VCM is accomplished at a temperatureof about 910 F. Steam in line 58 may be introduced into the bottom ofcoke drum 5 through lines 59 and 36 by opening valve 60 and closingvalve 37. Overhead valve 50 is closed and valve 48 is opened to permitthe steam and hydrocarbon vapors from coke drum 5 to pass through lines51, 61 and 62 and into a unit, not shown, for separating sour water fromintermediate gas oil. In a similar manner, by closing valves 38 and 49,and opening valves 63 and 54, steam in line 64 may be passed throughlines 65, 41, coke drum 6, and lines 55, 66, 67, and into an oil-waterseparating unit.

Cooling water enters at the top of the coke drum through lines not shownand discharges from the bottom. After the top and bottom covers areremoved from a coke drum, the petroleum coke inside is broken up by highimpact water jet and is removed through lines 68 and 69 at the bottom ofcoke drums 5 and 6 respectively. Lumps of petroleum coke clusters aresent to storage through line 70.

Altemately, when it is desirable to use the bottoms from thefractionating tower as the high boiling petroleum feed to the cokingheater, vacuum tower 17 may be removed from the line by closing valves13 and 25 and opening valve 12. Fractionator bottoms are then introduceddirectly into coking heater 29 by way of lines 14, 71, 72, 24, 27, and28.

EXAMPLE OF THE PREFERRED EMBODIMENTM M The following is ofiered in abetter understanding TABLE IV [Composition of charge stock tofractionator] Fluid cracked California Heavy- Fuel oilheav c cle SanArdo California reduced slops and carbon gas oil ith v crude crude crudenaphthas slurry catalyst g n itigty 0. 976-0. 983 0. 904-0. 947 0973-0.993 0. 904-0. 986 0. 994-1. 034 0. 973-1. 037

rscos y:

ssU t; F 15. GOO-22,000 500-3, 000 IOU-1,500 200-400 Table IV ContinuedTABLE IV [Composition of charge stock to fractlonator] C H H F l l Flgidcrackeld a l' or m eavy ue oi eav c e e San Ardo California reducedslops and carbon gas o i l vzith crude crude crude naphthas slurrycatalyst HSU at 210 l" HFHal. 122 F... Gravity, A1l Ash, wt. percent.

v Sulfur, wt. percent Conradson: carbon, wt. percent Carbon: soot, wt.percent Catalyst content, lbs/gal- Characterization factor, K..- 11.3-11 7 11. -11. 9 Salt content, crams bbl. 10-50 Usual volume range,percent 12-72 0-23 "Equal parts by weight 01 A120; and S102.

of the present invention, but the invention is not to be construed aslimited thereto.

With reference to the process shown in the drawing, a fresh feedstreamof about 60,300 BPSD* (*BPSD means barrels (42 gallons per barrel) perstandard operating day (24hours).) of mixed petroleum feedstocks asshown in Table 111 and having the properties as shown in Table IV isintroduced into a fractionator. In addition, about 26,180 BPSD ofhydrocarbon effluent vapor (basis feed to coke drum) and about 274 BPSDof steam are fed into the fractionator.

TABLE 111 Fresh Feed To Fractionatorw About 47,000 BPSD of high boilingpetroleum oil of about 12API from the bottom of the fractionator at atemperature of about 730 F. anda pressure of about 12 psig areintroduced into a vacuum tower. Other streams removed from thefractionator include: about 10,000 BPSD of intermediate gas oil of about28AP1 at a temperature of about 520 F.; about 12,000 BPSD of heavy gasoil of about 23AP1 and a temperature of about 690 F; about 11,000 BPSDof light gas oil of about 34AP1 and a temperature of about 415 F.; andabout 7,214 BPSD of miscellaneous and overhead products includingpropylene and butylene feedstocks, light and heavy naphtha, H 0, andfuel gas.

About 12,000 BPSD of vacuum gas oil are removed from the vacuum tower ata temperature of about 550 F. and a pressure of about 22 mm of mercury.Another stream of about 500 BPSD of vacuum gas oil is removed from thetower at a temperature of about 175 F. and a pressure of about 17 mm ofmercury. These two streams are combined yielding 12,500 BPSD of vacuumgas oil of about 17AP1.

34,000 BPSD of vacuum tower bottoms of about 3 to 7AP1, at a temperatureof about 690 F. and a pressure of about 30 mm of mercury are removedfrom the bottom of the vacuum tower and pumped at a pressure of about 55psig to the coking heater. Along the way about 274 BPSD of liquid waterare injected into the high boiling petroleum oil. The

coking heater is a 4 coil externally fired tubular heater. Each coil hasan inside diameter of 3% inches and is about 3,000 feet long. The vacuumtower bottoms feed stream is divided into four equal streams, one toeach coil. A pressure differential of about 250 psig across the coil isrequired to send the high boiling petroleum oil through the heating coilat a velocity of about 10 feet per second at the inlet and about feetper second at the outlet.

The effluent from the heater at a temperature of about 907 F. isintroduced into one of a pair of coke drums at a temperature of about885 F. and a pressure of about 45 psig. While one coke drum is beingfilled, the other is being decoked. The tum-around time for each cokedrum is about 28 hours. During the coking reaction about 26,180 BPSD ofeffluent vapors (basis feed to coking heater) and a relatively smallamount of water vapor (about 274 BPSD) are removed from the top of thecoke drum and passed to the fractionator as previously described.

After a coke drum is filled with coke to a desired level, it is takenout of service and decoked. About 15,000 pounds per hour of superheatedsteam is flowed then upwardly through the coke drum to displace residualhydrocarbon vapors and to remove any high boiling point hydrocarbonsremaining on the coke. The coke is steamed for about three hours oruntil the Volatile Combustible Matter (VCM) in weight percent is in therange of 8.0 to 29.5 and preferably in the range of 9.5 to l 1.0.

About 100,000 lbs/hr. of water are then flowed through the coke pit.Chunks of petroleum coke clusters are then separated from the water,removed from the coke pit, and transported by conveyor to the cokestorage area.

The coke pellet clusters may be broken into small lumps and used as isfor metallurgical purposes. Or, by calcining at a temperature of about1,000 to 1,500 C., the density of the coke may be increased and certainimpurities removed.

A visual examination of the product petroleum coke shows it to becomposed of subdivided solid carbon spheroidal pellets aboutone-thirty-second to one-fourth inch diameter loosely fused together ina cluster. A fraction of the clusters are ball-shaped with smoothpolished surfaces. Such balls may range in diameter from about 1 inch to6 inches-and are randomly dispersed throughout the coke drum.

The process of the invention has been described generally and byexamples with reference to various compositions of high boilingpetroleum oils, seed particles and nucleating agents, and various othermaterials of particular composition for purposes of clarity andillustration only. From the foregoing it would be apparent to thoseskilled in the art that the various modifications of the process, thematerials, and the amounts of the materials disclosed herein can be madewithout departure from the spirit of the invention.

We claim:

1. In the delayed coking process for producing petroleum coke, theimprovement for producing clusters of petroleum coke pellets whichcomprises: charging a distillation zone with petroleum oil and a slurryof liquid hydrocarbon and particulate carbon soot providing a minimum of0.01 weight percent of particulate carbon, recovering the liquid bottomsproduct from said distillation zone at a temperature above 690 F.,injecting 0.3 to 4.0 weight percent of liquid water into said liquidbottoms product and heating said mixture in a heating zone at atemperature in the range of about 650 to 930 F. for a limited time toeffect controlled cracking, and introducing the efiluent from saidheating zone into a coking zone where at a temperature in the range ofabout 800 to 895 F. and a pressure in the range of about 20 to 60 psiguncondensed hydrocarbon effluent vapor and steam are removed overhead,and where over a period of time with said particulate carbon soot actingas nucleating agents, petroleum coke pellets form and fuse together toform a cluster.

2. The process of claim 1 wherein the petroleum oil charged into thedistillation zone contains at least about 0.003 pounds of catalyst finescomprising aluminum oxide and silicon dioxide per gallon of petroleumoil.

3. The process of claim 1 wherein said liquid bottoms product from thedistillation zone is a hydrocarbon oil fraction from vacuum distillationhaving a 10 percent point at 10 mm Hg of at least 800 F.

050 v UNITED STAS PATE P 9) @FFECE CE TIFECA'E @F @QRQ'MfiN Patent No.3, 73, I Dated 79 97 Inventor) Warren G. Schlinger, Harold C. Kaufmanand Carr It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

l. Add the name of Carroll L. Crewley es e co-inventor. *3

2. Column 3, line 19 chan e "N to N Column 5, line 38 00035-09045 shouldbe re:-

errenged to line 37 in the column headed by Range 5. Column 6, line 2Change "opens" to open 7. Column 7, Table IV Under Sen Ardo Crude "6080" should read 60-80 8. Column 7, line 38 Change '02, O3, O4" to Signedand sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. Q ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents

2. The process of claim 1 wherein the petroleum oil charged into thedistillation zone contains at least about 0.003 pounds of catalyst finescomprising aluminum oxide and silicon dioxide per gallon of petroleumoil.
 3. The process of claim 1 wherein said liquid bottoms product fromthe distillation zone is a hydrocarbon oil fraction from vacuumdistillation having a 10 percent point at 10 mm Hg of at least 800* F.